More than £1m of cannabis and tobaccowas seized by Norfolk police at Gibbett Site Pig Farm in Hale Road, Bradenham, near Dereham. Picture: Ian Burt

A prolonged crackdown by police in London has forced growers and dealers to shift their operations out of the capital and into the regions – with East Anglia increasingly on the radar.

The criminals are also moving from industrial-scale factories to smaller operations – often in homes or outbuildings.

And police are concerned about the increasing strength of the cannabis that is being produced – often four or five times as strong as a few years ago.

The intensity of the battle between police and criminals is shown by the fact that in Norfolk, the number of crimes relating to cultivating cannabis has gone up from 91 in 2007 to 195 in 2012. The problem has hit the headlines in a major way recently:

Earlier this month, a cannabis factory was uncovered, with more than 900 plants, worth £500,000, being grown at a former cigar storage building in Nethergate Street, Bungay;

More than £1m of cannabis and tobacco was seized by Norfolk police following the discovery of one of the county’s largest cannabis farms in recent years at Bradenham, near Dereham, in November last year.

The offence of cultivating cannabis can cover anything from one plant to hundreds.

Colin Pearce, drugs availability liaison officer for Norfolk, said: “The number of cannabis plants seized has increased generally, but the counter balance to that is it demonstrates our commitment to finding these set-ups and dismantling them and we would always encourage the public to ring in with information about cannabis farms.”

Mr Pearce said Norfolk and Suffolk, like many other parts of the country, had experienced cannabis farms and factories being set up in the past 10 years or so following a concerted effort by the Metropolitan Police to crackdown on cannabis factories in the capital.

He said: “Historically they started in London about 10 to 12 years ago but as the Met became aware of them they moved out of more urban areas into rural areas.

“It’s just been a gradual spread out from London and eventually reached Norfolk and Suffolk.”

As well as organised Vietnamese groups growing cannabis there are also home-grown operations.

In 2011 five people involved in money laundering and running a sophisticated drugs factory in Thetford were sentenced to a total of more than 11 years in prison.

Thermal imaging cameras had highlighted heat over factory units in Roman Way in early December 2009 and officers from the protective services tactical crime unit had conducted a raid later in the month.

As officers tried to gain entry there was a strong smell of cannabis and during the search they discovered more than 750 cannabis plants growing there.

A sophisticated hydroponics network had been set up with the plants in all stages of development set out in the rooms inside the units.

Mr Pearce said that while it was difficult to say whether there were more large-scale factories than there used to be the cannabis being grown – whether in small or large numbers – was stronger than it ever was, which was another reason police were determined to put an end to it.

Anyone who suspects a building near them is being used as a cannabis factory should call Norfolk police on 101.